We would all identify the cause of a change in outcome to be whatever was changed in the initial conditions. In this case the changed conditions would be located inside the subject. So the cause for a change in outcome would be seen as located in the subject.
You're characterisation of the situation as external forces acting on the subject is misleading. We have in fact two distinct parts of the universe: the subject and its environment. How the situation evolves over time has to be the result of the interactions between these two parts. Presenting the situation as just external forces acting upon the subject is just wrong.
EB
I'm not following you. I still don't see how you have eliminated the possibility that your choices are not to some extent externally determined (which is what you need to do if you're attempting to satisfy your dictionary definition (post #7).
In our current understanding of nature, and outside any catastrophic situations such as a fire, a blast of radiations etc., what's physically going on inside a human being within the short window of time of a decision is essentially independent from his environment
as it is at that point in time. Obviously, we can travel back in time along the causality chain and quickly find external causes. These will indeed be external to the subject but only as he is at that point in the past, not at the time of the decision. At the time of the decision, in normal circumstances, the decision is all done essentially within the subject, and so independently of external forces.
And I'm not trying to eliminate possibilities. I'm just trying to articulate the best interpretation of free will I can think of. An interpretation that makes sense and that fits what most people say.
EB